Reduce to simplest form. $-\dfrac{1}{3}-\left(-\dfrac{3}{5}\right)=$
Answer: $=-{\dfrac{1\cdot 5}{3\cdot5}} +{\dfrac{3\cdot3}{5\cdot3}}$ $=-{\dfrac{5}{15}}+{\dfrac{9}{15}}$ $=\dfrac{4}{15}$